In certain medical conditions, it is advantageous to deliver a therapeutic agent directly to a target region to avoid medicating the entire body and to limit the amount of therapeutic agent required for effective treatment. Alternatively the same objective may be desirable for a diagnostic agent. One example of such a medical condition is an arterial thrombus, or clot, which can be treated effectively by localized application of such therapeutic fluids as those containing tissue plasminogen activator, urokinase, or streptokinase.
Infusion catheters have been developed which can deliver therapeutic fluids directly to affected bodily passages, for example a thrombotic region of an artery. One type of infusion catheter is a hollow tube, the distal end of which has been pierced through its side wall to form multiple openings, or ports, providing direct access to the exterior for fluid flowing through a common central lumen. The ports are disposed at several axial positions along the infusion section to provide distribution of the therapeutic fluid along a desired length of the bodily passage. However, fluids flowing through a tube flow more readily from ports offering the least flow resistance. The longer the flow path followed by the fluid in the central lumen, the higher the resistance and the higher the pressure drop (.DELTA.P) in the fluid. If the infusion section of this catheter has multiple ports or passageways the fluid flowing from each port exhibits resistance and a .DELTA.P proportional to the fluid flow distance along the length of the central lumen. Thus, the fluid flowing to the more distal ports experiences higher .DELTA.P than that flowing to the more proximal ports, and the fluid distribution is not uniform.
With respect to delivering various agents to specific regions of the body, the wall of a normal blood vessel includes an endothelial surface layer with an underlying connective tissue layer. When the wall of a blood vessel is diseased or injured, the endothelial surface layer breaks or tears. The break or lesion in the endothelial surface layer exposes collagenous connective tissue fibers to the blood flowing through the lumen of the blood vessel. Platelets present in the bloodstream adhere to the collagenous fibers, thereby initiating the coagulation cascade that results in a clot. The clot projects radially from the vessel wall into the lumen of the blood vessel and may cause turbulent flow.
Intravenous thrombolytic therapy breaks apart clots and restores laminar flow through the blood vessel and into other areas of the vascular system. Typically, intra-arterial thrombolytic therapy is provided by placing an infusion catheter or wire guide within the clotted lesion of a blood vessel so that a thrombolytic agent is infused into the vessel lumen in the region of the clot.
Conventional techniques utilize catheters and wire guides with multiple sideports intended for increasing the volume of the thrombolytic agent flowing into the bloodstream. For example, some infusion catheter sets include coaxially positioned inner and outer catheters, each with a number of sideports or infusion slits. Another coaxial infusion set includes an outer catheter with sideports and an inner wire guide with infusion holes. Yet other multiple sideport infusion sets include a catheter with sideports and a wire guide for extending through the lumen of the catheter and occluding the distal end hole of the catheter.
A problem with these multiple sideport devices is that most or all of the thrombolytic agent is diffused through only one or two proximal sideports, thereby limiting the surface area of the targeted blood vessel which could be treated by the released thrombolytic agent. As a result, the thrombolytic agent does not adequately mix with blood throughout the lesion. The relatively low concentration of the thrombolytic agent in the blood is insufficient to provide the desired therapeutic effect before being carried away in the bloodstream.
Furthermore, the uneven flow of the thrombolytic agent from the infusion sideports creates turbulence in the bloodstream. The turbulence can cause particles of the clot to fracture and flow farther along the arterial system into decreasing caliber blood vessels. Historically, treating tandem clots is more difficult and time consuming than the slow dissolution of one clot. Another difficulty encountered in treating a tandem clot is that the infusion device might not fit into the lumen of the blood vessel where the particle is wedged and occluding blood flow.